This invention relates to treatment of neoplastic cells utilizing viruses and viral vectors.
Neoplasia is a process by which the normal controlling mechanisms that regulate cell growth and differentiation are impaired resulting in progressive growth. During neoplasia, there is a characteristic failure to control cell turnover and growth. This lack of control causes a tumor to grow progressively, enlarging and occupying spaces in vital areas of the body. If the tumor invades surrounding tissue and is transported to distant sites the tendency of this tumor will be to result in death of the individual.
One-third of all individuals in the United States will develop cancer (American Cancer Society Yearly Outlook for 1990). The five year survival rate for these patients has risen to nearly 50% as a result of progress and early diagnosis and therapy of the disease (American Cancer Society Yearly Outlook for 1990). However, cancer remains second only to cardiac disease as a cause of death in this country (American Cancer Society Yearly Outlook for 1990). Nearly 20% of all Americans who die this year will die of cancer (American Cancer Society Yearly Outlook for 1990). Half of these deaths will be due to the three most common types of cancer: lung, breast, and colon.
Recently there has been a rapid expansion of cancer treatments. Even though new treatments are being developed, the need still exists for improved methods for the treatment of most types of cancers.
The preferential killing of cancer cells without deleterious effect on normal cells is the desired goal in cancer therapy. In the past this has been accomplished using a variety of procedures. These procedures include the administration of chemicals, chemotherapy, radiation, radiotherapy, and surgery.
Radiotherapy is a regional form of treatment used for the control of localized cancers (See Devita, V. T., in Harrison""s Principles of Internal Medicine, ed. Braunwald et al., 1987, McGraw-Hill Inc., New York, p. 431-446). Radiotherapy relies on the fact that some malignant diseases are more susceptible to damage by radiation. This difference in susceptibility depends on normal cells having a higher capacity for intercellular repair than neoplastic cells and the ability of normal organs to continue to function well if they are only segmentally damaged. If surrounding tissue can tolerate twice the radiation dose of a given tumor, then the tumor is radiosensitive. On the other hand, some tumors cannot be treated with radiotherapy. Cancer which extensively involves both lungs cannot be treated effectively with radiation therapy because of the greater radiosensitivity of the surrounding lung tissue (See Devita, V. T., in Harrison""s Principles of Internal Medicine, ed. Braunwald et al., 1987, McGraw-Hill Inc., New York, p. 431-446).
Surgery is still considered the primary treatment for most early cancers (See Devita, V. T., in Harrison""s Principles of Internal Medicine, ed. Braunwald et al., 1987, McGraw-Hill Inc., New York, p. 431-446). However, most tumors are operable but not fully resectable. Some tumors that appear resectable have micrometastatic disease outside the tumor field. This leads to a recurrence of the cancer close to the initial site of occurrence. Any cancer showing a level of metastasis effectively cannot be cured through surgery.
Other types of localized therapy (nonsystemic) have been explored. These include local hypothermia (Saleman et al., J. Neuro-Oncol. 1:225-236 (1983)), photodynamic therapy (Cheng et al., Surg. Neurol. 25:423-435 (1986)), and interstitial radiation (Gutin et al., J. Neurosurgery 67:864-873 (1987)). To date these therapies have been met with limited success.
Radiotherapy and surgery offer ways of reducing the tumor mass in specific regions of the body that are accessible through surgical techniques or high doses of radiotherapy. Neither is applicable to the destruction of widely disseminated or circulating tumors cells characteristically present in most patients with cancer. This is the stimulus of the development of systemic treatments of cancer such as chemotherapy.
The use of chemicals, even though widespread in use, has proved limitedly effective in treating most cancer types. One drawback to the use of cytotoxic agents for the treatment of cancer are their severe side effects. These include nausea, vomiting, CNS depression, localized pain, bone marrow depression, bleeding, renal damage, hypo and hyperglycemia and hypersensitivity reactions. Another drawback is that they are only effective against rapidly dividing cells.
A more modern approach to chemotherapy is to direct the toxic agents to the cancer cells themselves. This has been accomplished experimentally by linking the chemotherapeutic agent to either antibodies or toxic molecules that have a higher affinity for the tumor cells than normal cells. These directed toxic bullets are still in an .early clinical phase of development and are not commercially available.
Certain types of cancer, for example gliomas, which are the most common primary tumor arising in the human brain, defy the current modalities of treatment. Despite surgery, chemotherapy, and radiotherapy, glioblastoma multiforme, the most common of the gliomas is almost universally fatal (Schoenberg, B. S., xe2x80x9cThe epidemiology of nervous system tumors,xe2x80x9d in Oncology of the Nervous System, M. D. Walker, ed., Boston, Mass., Martinus Nijhoff (1983); Levin et al., xe2x80x9cNeoplasms of the Central Nervous System,xe2x80x9d Chapter 46, pp. 1557-1611, in Cancer: Principles and Practice of Oncology, vol. 2, 3rd ed., De Vita et al., eds., Philadelphia, Lippincott Press (1989)).
Gliomas represent nearly 40% of all primary brain tumors, with glioblastoma multiforme constituting the most malignant form (Schoenberg, B. S., xe2x80x9cThe epidemiology of nervous system tumors,xe2x80x9d in Oncology of the Nervous System, Walker, M. D., ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1983)). The five year survival rate for persons with this high grade type of astrocytoma is less than 5 percent given current treatment modalities of surgery, radiation therapy and/or chemotherapy (Mahaley et al., Neurosurgery 71:826-836 (1989); Schoenberg, B. S., xe2x80x9cThe epidemiology of nervous system tumors,xe2x80x9d in Oncology of the Nervous System, Walker, M. D., ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1983); Kim et al., J. Neurosurg. 74:27-37 (1991), Daumas-Duportet al., Cancer62:2152-2165 (1988)).
The resistance of glioblastomas to current chemotherapy may reflect the proliferative characteristics of this tumor type which are in-between lower grades of astrocytoma and other types of metastatic tumors in the central nervous system (CNS), (Nagashima and Hoshino, Acta Neuropathol. 66:12-17 (1985)). The bromodeoxyuridine labelling index, which measures the percentage of cells which are in S phase at any given moment, is 7.3% in glioblastoma tumors, which is 2 to 7 times higher than in lower grade astrocytomas, but less than in metastatic tumors (Nagashima and Hoshino, supra).
A related parameter that is useful for appreciating the relative resistance of glioblastomas to current therapeutic modalities is the growth fraction, or the relative proportion of cells proliferating in the tumor at any one time. The growth fraction in this tumor type is only 30%, with the remaining 70% of cells being in GO, a resting phase (cells in GO may die or may re-enter the active cell cycle; Yoshii et al., J. Neurosurg. 65:659-663 (1986)), while the 30% of glioblastoma cells that are actively dividing contribute to the lethal progression of this tumor, the 70% that are quiescent are responsible for the resistance of these tumors to a number of chemotherapeutic agents that target actively proliferating cells.
Further, surgical modalities for glioblastomas are hampered by the lack of distinct boundaries between the tumor and the surrounding parenchyma, and by the migration of tumor cells in the white matter tracts extending out from the primary site (Burger et al., J. Neurosurg. 58:159-169 (1983)), which preclude their complete removal.
Radiation therapy has also had limited success due to the low growth fraction in these tumor as well as to the radiation sensitivity of adjacent normal tissue (Wowra et al., Acta Neurochir. (Wien) 99:104-108 (1989); Zamorano et al., Acta Neurochir. Suppl. (Wien) 46:90-93 (1989)).
New approaches are needed to treat brain tumors. The herpes simplex virus type 1 (HSV) thymidine kinase (TK) gene has been introduced into retrovirus vectors to transfer conditional sensitivity to nucleoside analogues, such as ganciclovir, to lymphoma, sarcoma and murine adenocarcinoma cells in culture and in vito (Moolten, F. L., Cancer Res. 46:5276-5281 (1986); Moolten, F. L., et al., Human Gene Ther. 1:125-134 (1990); Plautz, G., et al., New Biol. 3:709-715 (1991); Moolten and Wells, J. Natl. Cancer Inst. 82:297-300 (1990)). Ganciclovir is a guanosine analogue that is specifically converted by HSV-TK to an intermediate capable of inhibiting DNA synthesis (Field, A. K., et al., Proc. Natl. Acad. Sci. USA 80:4139-4143 (1983)). Ezzedine et al. (New Biol. 3:608-614 (1991)) used a similar retrovirus vector, VIK, to transfer chemosensitivity to rat C6 glioma cells in culture and in vivo. The HSV-TK gene has also been used to mediate conditional toxicity in a number of other models, including cellular ablations in transgenic mice (Bernstein and Breitman, Mol. Biol. Med. 6:523-530 (1989); Borrelli et al., Proc. Natl. Acad. Sci. USA 85:7572-7576 (1988); Borrelli et al., Nature 339:538-541 (1989); Heyman et al., Proc. Natl. Acad. Sci. USA 86:2698-2702 (1989)).
Therefore a need exists for the development of a technique that will selectively destroy glioma while sparing normal brain cells. The present methods can be used universally for the selective destruction of all types of neoplastic cells.
Compositions and methods are provided for selectively killing neoplastic cells. In particular, retroviral vectors are utilized to target expression of a gene or gene product in neoplastic cells. Genes are selected whose gene products are capable of targeting cells for selective killing of tumor cells. The methods find particular use in the treatment of tumors of the nervous system.
The present inventors have discovered that retroviral vectors represent a novel strategy to deliver foreign genes with biological consequences to tumor cells.